Caption: Red blood cells and antibodies. Computer artwork of red blood cells (erythrocytes, red) and antibodies (immunoglobulins, Y-shaped) flowing through a blood vessel. Antibody molecules have two arms that can bind to specific antigens, for instance viral or bacterial proteins. In doing this they mark the antigen for destruction by phagocytes, white blood cells that ingest and destroy foreign bodies. Antibodies can also kill some pathogens directly and can neutralise toxins.